Chain type energy storage system low voltage ride through control method and system

Abstract

The application relates to a low-voltage ride-through control method and system of a chain energy storage system, which comprises the following steps: obtaining output voltage reference values of each phase branch of the chain energy storage system; determining zero sequence voltages that need to be compensated by the chain energy storage system to the power grid based on the average values of the DC side voltages of all chain links in the chain energy storage system and the average values of the DC side voltages of the chain links in each phase branch of the chain energy storage system; obtaining the modulation voltages of each chain link in the chain energy storage system by adopting a low-voltage ride-through control strategy based on the output voltage reference values and the zero sequence voltages; and modulating the modulation voltages of each chain link in the chain energy storage system to generate pulse signals used for controlling the on-off of internal power devices of each chain link in the chain energy storage system in the low-voltage ride-through process. The technical scheme provided by the application can realize power distribution among phases and in a phase, maintain the DC side voltages of each chain link, improve dynamic response, and guarantee the low-voltage ride-through operation capability of the system.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a low-voltage ride-through control method and system for chain-type energy storage systems. Background Technology

[0002] With increasing energy demand and the development of power electronics technology, high-power, high-performance multilevel converters have been widely used in power systems. Cascaded multilevel circuits have advantages such as easy modular design, high reliability, high efficiency, and low switching frequency. At the same time, the switching devices in this topology have low voltage stress, and fewer power semiconductor devices are required to generate the same number of levels. Therefore, they are widely used in static var compensators, active power filters, power electronic transformers, and other applications.

[0003] Chained energy storage systems, as an extension of cascaded multilevel circuits, can output reactive power to the grid to compensate for grid imbalances when voltage drops occur. However, the operating capability of chained energy storage systems is limited by DC-side voltage balance; the better the DC-side voltage balance, the stronger the operating capability. Therefore, in-depth research on power control methods for chained energy storage systems is urgently needed.

[0004] Currently, there are two main approaches to controlling chain-type energy storage systems. One approach is to use the traditional phase-to-phase DC voltage balancing strategy, but this strategy does not take into account the situation of grid voltage imbalance. The other approach is to use a compensation method based on zero-sequence voltage or negative-sequence current, but this method is mainly based on open-loop calculations, and its accuracy and dynamic response cannot meet the requirements for low-voltage ride-through.

[0005] Therefore, no technology has yet been proposed that can solve the above problems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to propose a low-voltage ride-through control method and system for a chain-type energy storage system under unbalanced grid faults. This method can achieve phase-to-phase and phase-to-phase power distribution under unbalanced grid faults, maintain the DC-side voltage of each chain link, and improve dynamic response, thus ensuring the system's low-voltage ride-through capability.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This invention proposes a low-voltage ride-through control method for a chain-type energy storage system under grid imbalance faults, the method comprising:

[0009] Obtain the reference values ​​of the output voltage of each phase branch of the chain energy storage system;

[0010] Based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system, the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid is determined.

[0011] Based on the output voltage reference values ​​of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, the modulation voltage of each link in the chain energy storage system is obtained by adopting a low voltage ride-through control strategy.

[0012] The modulation voltage of each link in the chain energy storage system is modulated to generate pulse signals used to control the on / off switching of power devices inside each link of the chain energy storage system during low voltage ride-through.

[0013] This invention proposes a low-voltage ride-through control system for a chain-type energy storage system under grid imbalance faults, the system comprising:

[0014] The first acquisition module is used to acquire the output voltage reference values ​​of each phase branch of the chain energy storage system;

[0015] The determination module is used to determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system.

[0016] The second acquisition module is used to obtain the modulation voltage of each link in the chain energy storage system based on the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, using a low voltage ride-through control strategy.

[0017] The generation module is used to modulate the modulation voltage of each link in the chain energy storage system and generate pulse signals to control the on / off switching of the power devices inside each link of the chain energy storage system during low voltage ride-through.

[0018] Compared with the closest existing technology, the present invention has the following advantages:

[0019] The technical solution provided by this invention obtains the output voltage reference values ​​of each phase branch of a chain energy storage system; based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system, it determines the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid; based on the output voltage reference values ​​of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, it adopts a low-voltage ride-through control strategy to obtain the modulation voltage of each link in the chain energy storage system; it modulates the modulation voltage of each link in the chain energy storage system to generate pulse signals used to control the on / off switching of power devices inside each link of the chain energy storage system during low-voltage ride-through. This solution can achieve phase-to-phase and phase-to-phase power distribution under unbalanced grid faults, maintain the DC-side voltage of each link, improve dynamic response, and ensure the system's low-voltage ride-through capability. Attached Figure Description

[0020] Figure 1 This is a structural diagram of a chain energy storage system;

[0021] Figure 2 This is a flowchart of a low-voltage ride-through control method for a chain-type energy storage system under grid imbalance faults.

[0022] Figure 3 This is a block diagram of low voltage ride-through control for a chain energy storage system;

[0023] Figure 4 This is a schematic diagram of reactive / active current control in an embodiment of the present invention;

[0024] Figure 5 This is a block diagram of zero-sequence voltage injection control in an embodiment of the present invention;

[0025] Figure 6 This is a structural diagram of a low-voltage ride-through control system for a chain-type energy storage system under grid imbalance faults.

[0026] Figure 7 This is a simulation result diagram of the power grid voltage in an embodiment of the present invention;

[0027] Figure 8 This is a simulation result diagram of the DC side voltage of the capacitor chain segment in an embodiment of the present invention;

[0028] Figure 9 This is a simulation result diagram of the zero-sequence voltage in an embodiment of the present invention;

[0029] Figure 10 This is a simulation result diagram of the output current in an embodiment of the present invention. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] Depend on Figure 1 The chain-type energy storage system shown is connected to the power grid via a filter inductor. Each phase branch of the chain-type energy storage system consists of N capacitor links, where L is the value of the filter inductor, and v... dc V is the DC-side voltage of the link. a v b v c These are the a, b, and c phase voltages of the power grid, i. a i b i c These are the currents of phases a, b, and c of the power grid, respectively.

[0034] Due to the structural characteristics of chain-type energy storage systems, when an imbalance fault occurs in the power grid, low-voltage ride-through control can be implemented on the chain-type energy storage system to enable it to provide reactive power compensation to the power grid.

[0035] In view of this, the present invention provides a low-voltage ride-through control method for a chain-type energy storage system under grid imbalance faults, such as... Figure 2 As shown, it includes:

[0036] Step 101: Obtain the reference values ​​of the output voltage of each phase branch of the chain energy storage system;

[0037] Step 102: Based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system, determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid.

[0038] Step 103: Based on the output voltage reference values ​​of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, the modulation voltage of each link in the chain energy storage system is obtained by adopting a low voltage ride-through control strategy.

[0039] Step 104: Modulate the modulation voltage of each link in the chain energy storage system to generate pulse signals used to control the on / off switching of power devices inside each link of the chain energy storage system during low voltage ride-through.

[0040] In an embodiment of the present invention, when an asymmetrical voltage drop fault occurs in the power grid, the grid voltage contains positive sequence components and negative sequence components, which generate different active power with the current of each phase, causing power flow between the three phases, affecting the DC side voltage balance of each phase, and causing the output current of the chain energy storage system to be unable to track the command.

[0041] According to such Figure 3 The low-voltage ride-through control block diagram of the chain energy storage system shown is used to control and complete the entire low-voltage ride-through process. The control block diagram consists of a reactive / active current control section executing step 101, a zero-sequence voltage injection section executing step 102, an independent voltage balance control section executing step 103, and a carrier phase-shift modulation section executing step 104. In the figure, v m,ref V is the reference value for the output voltage of the m-phase branch of the chain energy storage system. mn,ref v is the modulation voltage of the nth link in the m-phase branch of the chain energy storage system. mM,ref This represents the phase voltage modulation value of the m-phase branch in the chain energy storage system.

[0042] Specifically, step 101 includes:

[0043] The process of obtaining the output voltage reference value of each phase branch of the chain energy storage system includes:

[0044] Step I: Determine the positive d-sequence component, positive q-sequence component, negative d-sequence component, and negative q-sequence component of the grid current based on the three-phase current of the grid, and determine the positive d-sequence component, positive q-sequence component, negative d-sequence component, and negative q-sequence component of the grid voltage based on the three-phase voltage of the grid.

[0045] Step II: Substitute the difference between the DC-side voltage setpoint of the chain link in the chain energy storage system and the average DC-side voltage of all chain links in the chain energy storage system into the PI controller to obtain the setpoint of the positive sequence component of the grid current on the q-axis.

[0046] Step III: Substitute the positive d-sequence component, positive q-sequence component, negative d-sequence component, and negative q-sequence component of the grid voltage, the positive d-sequence component, positive q-sequence component, negative d-sequence component, and negative q-sequence component of the grid current, as well as the given values ​​of the positive q-sequence component, positive d-sequence component, negative q-sequence component, and negative d-sequence component of the grid current into the current closed-loop controller to obtain the output voltage reference values ​​of each phase branch of the chain energy storage system.

[0047] In the embodiments of the present invention, the reactive / active current control part of executing step 101 will be described in detail:

[0048] The reactive / active current control section is divided into three stages. The first stage is the extraction of the positive and negative sequence components of voltage and current under fault conditions. This stage includes:

[0049] Let V p V represents the magnitude of the positive-sequence component of the grid voltage. n I represents the magnitude of the negative sequence component of the grid voltage. p I is the amplitude of the positive sequence component of the grid current. n Let θ1 be the amplitude of the negative-sequence component of the grid current, θ2 be the phase of the positive-sequence component of the grid voltage, and θ3 be the phase of the negative-sequence component of the grid voltage. p Let θ be the phase of the positive sequence component of the grid current. n This represents the phase of the negative sequence component of the grid current.

[0050] That is, it is always present:

[0051]

[0052] To extract the positive and negative sequence components of voltage and current under fault conditions, the positive sequence component of the grid voltage on the d-axis is obtained by solving the following formula. The positive q-sequence component of the grid voltage

[0053]

[0054] Solving the following formula yields the d-axis negative sequence component of the grid voltage. negative q-axis component of grid voltage

[0055]

[0056] Solving the following formula yields the d-axis positive sequence component of the grid current. and the positive q-sequence component of the grid current

[0057]

[0058] Solving the following formula yields the d-axis negative sequence component of the grid current. negative q-axis component of grid current

[0059]

[0060] In the formula, T αβ-pos T is the positive-order component transformation matrix between the αβ coordinate system and the dq coordinate system. αβ-neg Let v be the negative order component transformation matrix between the αβ coordinate system and the dq coordinate system. α The grid voltage along the α-axis, v β Let i be the β-axis grid voltage.α Let i be the α-axis grid current. β This refers to the β-axis grid current.

[0061] Solving the following formula yields v α and v β :

[0062]

[0063] Solving the following formula yields i α and i β :

[0064]

[0065] In the formula, T abc-αβ Let v be the transformation matrix between the abc coordinate system and the αβ coordinate system. a Let V be the voltage of phase a of the power grid. b V is the voltage of phase b of the power grid. c Let i be the voltage of phase c of the power grid. a Let i be the phase current of the power grid. b Let i be the phase b current of the power grid. c This refers to the c-phase current of the power grid.

[0066] T is determined by the following formula abc-αβ :

[0067]

[0068] T is determined by the following formula αβ-pos :

[0069]

[0070] T is determined by the following formula αβ-neg :

[0071]

[0072] In the formula, w is the power grid frequency, and t is the current time.

[0073] The second stage is the reactive / active current command calculation stage, and its corresponding reactive / active current command calculation block diagram is as follows: Figure 4 As shown, it includes:

[0074] The average value of all collected DC-side voltages of the links is used as the feedback value of the PI controller in the calculation of reactive / active current commands. The error between the PI controller and the reference value of the DC-side voltage of the links is calculated. The active current setpoint is obtained through PI (proportional-integral) control, and the reactive current setpoint is obtained through the operating requirements of the equipment.

[0075] When a suitable zero-sequence voltage is used for compensation, the three-phase current contains only positive sequence current, so the reactive / active current setpoint also contains only positive sequence current.

[0076] The third stage is the current closed-loop control stage, which includes:

[0077] The positive and negative sequence components of voltage and current under fault conditions, along with the reactive / active current setpoints, are used for current closed-loop control to obtain the output voltage reference values ​​of each phase branch of the chain energy storage system, enabling the output reactive / active current to track the command values.

[0078] In a chain-type energy storage system, each link outputs reactive current that meets the grid's requirements, and enables each link in the chain-type energy storage system to generate active current that compensates for its own switching losses.

[0079] Specifically, step 102 includes:

[0080] Step 102-1: Obtain the unbalanced power of each phase branch of the chain energy storage system;

[0081] Step 102-2: Substitute the difference between the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system into the PI controller to obtain the active power compensated to the grid by each phase branch of the chain energy storage system.

[0082] Step 102-3: Calculate the difference between the active power compensated to the grid by each phase branch of the chain energy storage system and the unbalanced power of each phase branch of the chain energy storage system, and use the difference as the active power control command value of each phase branch of the chain energy storage system.

[0083] Step 102-4: Determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate the grid using the active power control command value of each phase branch of the chain energy storage system.

[0084] In an embodiment of the present invention, the zero-sequence voltage injection portion of performing step 102 will be described in detail; the control block diagram of the zero-sequence voltage injection portion is as follows: Figure 5 As shown, it mainly includes a coordinated control link between the phase-to-phase voltage balance control link and the power feedforward control link. The zero-sequence voltage that needs to be compensated is calculated through the coordinated control of the phase-to-phase voltage balance control and the power feedforward control link, so as to realize the phase-to-phase power redistribution.

[0085] In the power feedforward control stage, the unbalanced power generated by each phase branch of the chain energy storage system under an unbalanced power grid is calculated.

[0086] Power feedforward control uses the unbalanced power generated by unbalanced voltage and current in each phase as the feedforward quantity for voltage balance control, so as to improve the dynamic response of the system.

[0087] The phase-to-phase voltage balance control circuit compares the average DC-side voltage of each link in each phase branch with the average DC-side voltage of all links, and calculates the corresponding compensated active power P through PI control. CBm,FB After correction using feedforward parameters, the active power command for phase-to-phase voltage balance control is obtained.

[0088]

[0089] After obtaining the active power commands for each corresponding compensation, the three-phase commands are transformed to the α-β coordinate system through coordinate transformation to obtain the zero-sequence voltage amplitude and phase that meet the compensation requirements, and thus obtain the zero-sequence voltage that needs to be compensated.

[0090] When the power grid imbalance is determined, the imbalance power of each phase can be determined, and the zero-sequence voltage value that uniquely meets the compensation requirements can be obtained, thus enabling low-voltage ride-through operation.

[0091] Furthermore, step 102-1 includes:

[0092] The unbalanced power P of the m-phase branch of the chain energy storage system is determined by the following formula. CBm,FF :

[0093]

[0094] In the formula, This represents the positive q-sequence component of the grid voltage. The given value is the q-axis positive sequence component of the grid current. This represents the negative q-sequence component of the grid voltage. The given value is the q-axis negative sequence component of the grid current. The positive sequence component of the grid voltage along the d-axis. The given value is the positive sequence component of the d-axis of the grid current. This represents the negative d-sequence component of the grid voltage. Given the negative sequence component of the grid current along the d-axis, v m Let i be the m-phase voltage of the power grid. m Let m be the m-phase current of the power grid, T be the adjustment duration, τ be the initial time of the last adjustment, and m = a, b, c.

[0095] In an optional embodiment of the present invention, power feedforward control can be used to improve the dynamic response speed of intra-phase voltage regulation.

[0096] Furthermore, step 102-4 includes:

[0097] The zero-sequence voltage v that the m-phase branch of the chain energy storage system needs to compensate the grid for is determined by the following formula. OM :

[0098] v OM =V OM cos(wt+γ)

[0099] In the formula, V OM γ is the amplitude of the zero-sequence voltage that the m-phase branch of the chain energy storage system needs to compensate to the grid, w is the grid frequency, and t is the current time.

[0100] V is determined by the following formula. OM and γ:

[0101]

[0102] In the formula, This represents the active power control command value for the α-axis. This is the active power control command value for the β-axis. The given value is the q-axis positive sequence component of the grid current. The given value is the q-axis negative sequence component of the grid current. The given value is the positive sequence component of the d-axis of the grid current. The given value is the negative sequence component of the d-axis of the grid current;

[0103] Wherein, determined by the following formula and

[0104]

[0105] In the formula, T abc-αβ Let be the transformation matrix between the abc coordinate system and the αβ coordinate system. These are the active power control command values ​​for phases a, b, and c of the power grid, respectively.

[0106] An optional embodiment of the present invention is to use a zero-sequence voltage injection method to eliminate the influence of negative-sequence current on interphase power imbalance and maintain interphase power balance.

[0107] Specifically, step 103 includes:

[0108] Step 103-1: Based on the DC-side voltage of each link in the chain energy storage system and the average DC-side voltage of each link in each phase branch of the chain energy storage system, a voltage balance control strategy is adopted to determine the bias voltage of each link in the chain energy storage system.

[0109] Step 103-2: Based on the bias voltage of each link in the chain energy storage system, the reference value of the output voltage of each phase branch of the chain energy storage system, and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, calculate the modulation voltage of each link in the chain energy storage system.

[0110] The independent voltage balance control section of step 103 is explained in detail. After obtaining the total output voltage reference value for each phase link, independent DC-side voltage balance control is performed on each phase link. The DC-side voltage of each link is compared with the average DC-side voltage within the phase. The compensation amount (bias voltage) of the output voltage of each link is adjusted by proportional control. The compensation amount is combined with the voltage reference value allocated to each link, and a switching signal is generated by carrier phase-shift modulation to achieve link charging and discharging balance, stabilize the DC-side voltage, and enable the system to operate stably under grid imbalance fault conditions, achieving low-voltage ride-through.

[0111] Furthermore, step 103-1 includes:

[0112] The bias voltage v of the nth link in the m-phase branch of the chain energy storage system is determined by the following formula. IB.mn :

[0113]

[0114] In the formula, v dc.m V represents the average DC-side voltage of a link in the m-phase branch of a chain energy storage system. dc.mn Let be the DC-side voltage of the nth link in the m-phase branch of the chain energy storage system, kp be the proportionality coefficient, m = a, b, c, n ∈ (1 ~ N), and N be the total number of links in each phase branch of the chain energy storage system.

[0115] Furthermore, step 103-2 includes:

[0116] Step 103-2-1: The ratio of the sum of the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid to the total number of chain links contained in each phase branch of the chain energy storage system is used as the phase voltage modulation value of each phase branch of the chain energy storage system.

[0117] Step 103-2-2: The sum of the phase voltage modulation value of each phase branch of the chain energy storage system and the bias voltage of each link in the chain energy storage system is used as the modulation voltage of that link.

[0118] Specifically, step 104 includes:

[0119] Carrier phase-shift modulation technology is used to modulate the modulation voltage of each link in the chain energy storage system.

[0120] The technical solution provided by this invention is applicable to chain-type energy storage systems, enabling phase-to-phase power balance and intra-phase power distribution under unbalanced grid faults, ensuring the system's low-voltage ride-through capability. Furthermore, the application of this solution is not limited to star-connected three-phase cascaded multilevel circuits with capacitors as DC-side voltage sources; theoretically, it is also applicable to other cascaded multilevel circuits.

[0121] Example 2:

[0122] This invention provides a low-voltage ride-through control system for a chain-type energy storage system under grid imbalance faults, wherein the... Figure 6 As shown, the system includes:

[0123] The first acquisition module is used to acquire the output voltage reference values ​​of each phase branch of the chain energy storage system;

[0124] The determination module is used to determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system.

[0125] The second acquisition module is used to obtain the modulation voltage of each link in the chain energy storage system based on the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, using a low voltage ride-through control strategy.

[0126] The generation module is used to modulate the modulation voltage of each link in the chain energy storage system and generate pulse signals to control the on / off switching of the power devices inside each link of the chain energy storage system during low voltage ride-through.

[0127] Specifically, the determining module includes:

[0128] The first acquisition unit is used to acquire the unbalanced power of each phase branch of the chain energy storage system;

[0129] The second acquisition unit is used to substitute the difference between the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system into the PI controller to obtain the active power compensated to the grid by each phase branch of the chain energy storage system.

[0130] The first calculation unit is used to calculate the difference between the active power compensated to the grid by each phase branch of the chain energy storage system and the unbalanced power of each phase branch of the chain energy storage system, and to use the difference as the active power control command value of each phase branch of the chain energy storage system.

[0131] The first determining unit is used to determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid using the active power control command value of each phase branch of the chain energy storage system.

[0132] Furthermore, obtaining the unbalanced power of each phase branch of the chain energy storage system includes:

[0133] The unbalanced power P of the m-phase branch of the chain energy storage system is determined by the following formula. CBm,FF :

[0134]

[0135] In the formula, This represents the positive q-sequence component of the grid voltage. The given value is the q-axis positive sequence component of the grid current. This represents the negative q-sequence component of the grid voltage. The given value is the q-axis negative sequence component of the grid current. The positive sequence component of the grid voltage along the d-axis. The given value is the positive sequence component of the d-axis of the grid current. This represents the negative d-sequence component of the grid voltage. Given the negative sequence component of the grid current along the d-axis, v m Let i be the m-phase voltage of the power grid. m Let m be the m-phase current of the power grid, T be the adjustment duration, τ be the initial time of the last adjustment, and m = a, b, c.

[0136] Furthermore, the first determining unit is configured to:

[0137] The zero-sequence voltage v that the m-phase branch of the chain energy storage system needs to compensate the grid for is determined by the following formula. OM :

[0138] v OM =V OM cos(wt+γ)

[0139] In the formula, V OM γ is the amplitude of the zero-sequence voltage that the m-phase branch of the chain energy storage system needs to compensate to the grid, w is the grid frequency, and t is the current time.

[0140] V is determined by the following formula. OM and γ:

[0141]

[0142] In the formula, This represents the active power control command value for the α-axis. This is the active power control command value for the β-axis. The given value is the q-axis positive sequence component of the grid current. The given value is the q-axis negative sequence component of the grid current. The given value is the positive sequence component of the d-axis of the grid current. The given value is the negative sequence component of the d-axis of the grid current;

[0143] Wherein, determined by the following formula and

[0144]

[0145] In the formula, T abc-αβ Let be the transformation matrix between the abc coordinate system and the αβ coordinate system. These are the active power control command values ​​for phases a, b, and c of the power grid, respectively.

[0146] Specifically, the second acquisition module is used for:

[0147] The second determining unit is used to determine the bias voltage of each link in the chain energy storage system based on the DC side voltage of each link in the chain energy storage system and the average DC side voltage of each link in each phase branch of the chain energy storage system, using a voltage balance control strategy.

[0148] The second calculation unit is used to calculate the modulation voltage of each link in the chain energy storage system based on the bias voltage of each link in the chain energy storage system, the reference value of the output voltage of each phase branch of the chain energy storage system, and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid.

[0149] Furthermore, the second determining unit is used for:

[0150] The bias voltage v of the nth link in the m-phase branch of the chain energy storage system is determined by the following formula. IB.mn :

[0151]

[0152] In the formula, v dc.m V represents the average DC-side voltage of a link in the m-phase branch of a chain energy storage system. dc.mn Let be the DC-side voltage of the nth link in the m-phase branch of the chain energy storage system, kp be the proportionality coefficient, m = a, b, c, n ∈ (1 ~ N), and N be the total number of links in each phase branch of the chain energy storage system.

[0153] Furthermore, the second computing unit includes:

[0154] The first defined subunit is used to take the ratio of the sum of the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid to the total number of chain links contained in each phase branch of the chain energy storage system as the phase voltage modulation value of each phase branch of the chain energy storage system.

[0155] The second definition subunit is used to sum the phase voltage modulation value of each phase branch of the chain energy storage system with the bias voltage of each link in the chain energy storage system as the modulation voltage of that link.

[0156] Specifically, the generation module is used for:

[0157] Carrier phase-shift modulation technology is used to modulate the modulation voltage of each link in the chain energy storage system.

[0158] Example 3:

[0159] To verify the effectiveness of this invention, an experimental simulation model of the chain energy storage system was built in Matlab / Simulink. The actual parameters and equivalent parameters are shown in Table 1.

[0160] Table 1

[0161] parameter symbol numerical values Chain link rated voltage <![CDATA[V dc ]]> 783V DC side capacitor C 4.8mF Number of links in each phase N 3 Switching frequency <![CDATA[f s ]]> 2KHz Grid phase voltage <![CDATA[v s ]]> 20.2kV Filter inductor <![CDATA[L s ]]> 60mH

[0162] Figure 7 The following is a diagram showing the simulation results of the power grid voltage in an embodiment of the present invention. Figure 8 The following is a simulation result diagram of the DC side voltage of the capacitor link in the embodiment of the present invention. Figure 9 The following is a simulation result diagram of the zero-sequence voltage in an embodiment of the present invention. Figure 10 This is a simulation result diagram of the output current in an embodiment of the present invention;

[0163] As shown in the figure above, the voltage of phase A of the power grid drops by 50% within 0.3-0.5 seconds. Under the control of the controller, the system generates a zero-sequence voltage to compensate for the unbalanced power generated by the grid voltage. By injecting a suitable zero-sequence voltage, the DC-side capacitor voltage of each link remains stable during the fault, and the output current remains unchanged, containing only positive-sequence components. Simulation results show that the control method proposed in this invention is effective, has good dynamic response, and can meet the low-voltage ride-through capability of the equipment under grid fault conditions.

[0164] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0165] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0166] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0167] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A low-voltage ride-through control method for a chain-type energy storage system under grid imbalance faults, characterized in that, The method includes: Obtain the reference values ​​of the output voltage of each phase branch of the chain energy storage system; Based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system, the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid is determined. Based on the output voltage reference values ​​of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, the modulation voltage of each link in the chain energy storage system is obtained by adopting a low voltage ride-through control strategy. The modulation voltage of each link in the chain energy storage system is modulated to generate pulse signals used to control the on / off switching of power devices inside each link of the chain energy storage system during low voltage ride-through. The determination of the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate the grid based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system includes: To obtain the unbalanced power of each phase branch of the chain energy storage system; The difference between the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system is substituted into the PI controller to obtain the active power compensated to the grid by each phase branch of the chain energy storage system. Calculate the difference between the active power compensated to the grid by each phase branch of the chain energy storage system and the unbalanced power of each phase branch of the chain energy storage system, and use the difference as the active power control command value of each phase branch of the chain energy storage system. The zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate the grid is determined by using the active power control command value of each phase branch.

2. The method as described in claim 1, characterized in that, The acquisition of the unbalanced power of each phase branch of the chain energy storage system includes: The unbalanced power of the m-phase branch of the chain energy storage system is determined by the following formula. : In the formula, This represents the positive q-sequence component of the grid voltage. The given value is the q-axis positive sequence component of the grid current. This represents the negative q-sequence component of the grid voltage. The given value is the q-axis negative sequence component of the grid current. The positive sequence component of the grid voltage along the d-axis. The given value is the positive sequence component of the d-axis of the grid current. This represents the negative d-sequence component of the grid voltage. The given value is the negative sequence component of the d-axis of the grid current. Let m be the voltage of the power grid. Let m be the current of the power grid. To adjust the duration, This is the initial time of the last adjustment. .

3. The method as described in claim 1, characterized in that, The determination of the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate the grid for using the active power control command values ​​of each phase branch includes: The zero-sequence voltage that the m-phase branch of the chain energy storage system needs to compensate the grid for is determined by the following formula. : In the formula, Let be the magnitude of the zero-sequence voltage that the m-phase branch of the chain energy storage system needs to compensate the grid for. The phase of the zero-sequence voltage that the m-phase branch of the chain energy storage system needs to compensate to the grid. For the power grid frequency, The current moment; Wherein, determined by the following formula and : In the formula, for Shaft active power control command value, for Shaft active power control command value, The given value is the q-axis positive sequence component of the grid current. The given value is the q-axis negative sequence component of the grid current. The given value is the positive sequence component of the d-axis of the grid current. The given value is the negative sequence component of the d-axis of the grid current; Wherein, determined by the following formula and : In the formula, for coordinate system and Transformation matrices between coordinate systems , , These are the active power control command values ​​for phases a, b, and c of the power grid, respectively.

4. The method as described in claim 1, characterized in that, Based on the output voltage reference values ​​of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, a low-voltage ride-through control strategy is adopted to obtain the modulation voltage of each link in the chain energy storage system, including: Based on the DC-side voltage of each link in the chain energy storage system and the average DC-side voltage of each link in each phase branch of the chain energy storage system, a voltage balance control strategy is adopted to determine the bias voltage of each link in the chain energy storage system. Based on the bias voltage of each link in the chain energy storage system, the reference value of the output voltage of each phase branch of the chain energy storage system, and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, the modulation voltage of each link in the chain energy storage system is calculated.

5. The method as described in claim 4, characterized in that, The bias voltage of each link in the chain energy storage system is determined using a voltage balance control strategy based on the DC-side voltage of each link in the chain energy storage system and the average DC-side voltage of each link in each phase branch of the chain energy storage system. This includes: The m-th phase in the chain energy storage system is determined by the following formula. Bias voltage of each link : In the formula, This represents the average DC-side voltage of each link in the m-phase branch of the chain energy storage system. In the m-phase branch of the chain energy storage system, the first DC-side voltage of each link, This is the proportionality coefficient. , , The total number of chain links in each phase branch of a chain-type energy storage system.

6. The method as described in claim 4, characterized in that, The method for calculating the modulation voltage of each link in the chain energy storage system, based on the bias voltage of each link in the chain energy storage system, the reference value of the output voltage of each phase branch of the chain energy storage system, and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, includes: The ratio of the sum of the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid to the total number of chain links contained in each phase branch of the chain energy storage system is used as the phase voltage modulation value of each phase branch of the chain energy storage system. The modulation voltage of a link is the sum of the phase voltage modulation value of each phase branch of the chain energy storage system and the bias voltage of each link in the chain energy storage system.

7. The method as described in claim 1, characterized in that, The modulation of the modulation voltage of each link in the chain energy storage system generates pulse signals for controlling the on / off switching of power devices within each link of the chain energy storage system during low-voltage ride-through, including: Carrier phase-shift modulation technology is used to modulate the modulation voltage of each link in the chain energy storage system.

8. A low-voltage ride-through control system for a chain-type energy storage system under grid imbalance faults, characterized in that, The system includes: The first acquisition module is used to acquire the output voltage reference values ​​of each phase branch of the chain energy storage system; The determination module is used to determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid based on the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system. The second acquisition module is used to obtain the modulation voltage of each link in the chain energy storage system based on the output voltage reference value of each phase branch of the chain energy storage system and the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid, using a low voltage ride-through control strategy. The generation module is used to modulate the modulation voltage of each link in the chain energy storage system and generate pulse signals to control the on / off switching of the power devices inside each link of the chain energy storage system during low voltage ride-through. The determining module includes: The first acquisition unit is used to acquire the unbalanced power of each phase branch of the chain energy storage system; The second acquisition unit is used to substitute the difference between the average DC-side voltage of all links in the chain energy storage system and the average DC-side voltage of the links in each phase branch of the chain energy storage system into the PI controller to obtain the active power compensated to the grid by each phase branch of the chain energy storage system. The first calculation unit is used to calculate the difference between the active power compensated to the grid by each phase branch of the chain energy storage system and the unbalanced power of each phase branch of the chain energy storage system, and to use the difference as the active power control command value of each phase branch of the chain energy storage system. The first determining unit is used to determine the zero-sequence voltage that each phase branch of the chain energy storage system needs to compensate to the grid using the active power control command value of each phase branch of the chain energy storage system.

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